You probably don’t give your kidneys much thought. When they’re working well, they filter your blood and help you get rid of waste products from the food you eat. Most everyone has two kidneys, one on each side of your back and below your ribs. Each kidney provides about 750,000 filters that work around the clock to clean your blood and eliminate water.
Your kidneys also control the levels of various substances in your blood: salt, potassium, and acid, as well as phosphorus and calcium, which help to build strong bones. They also make a hormone that tells your body to produce red blood cells from bone marrow.
Kidney function is measured by “creatinine,” a chemical that comes from muscle and is cleared through the kidneys. When the kidneys are functioning properly, the creatinine level is low; it begins to rise when the kidneys are not able to do their job.